Acids, Bases & Salts
pH, neutralisation reactions, and preparation of salts
Acids release H⁺ ions in water. Bases accept H⁺ ions (or release OH⁻ ions). Alkalis are soluble bases.
pH scale: 0-6 = acid, 7 = neutral, 8-14 = alkali. pH 7 = pure water.
Indicators:
- Litmus: red in acid, blue in alkali
- Universal indicator: full colour range, gives approximate pH
- Phenolphthalein: colourless in acid, pink in alkali
Neutralisation: acid + base → salt + water
- HCl + NaOH → NaCl + H₂O
- H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
Preparing salts:
- Acid + metal: H₂SO₄ + Zn → ZnSO₄ + H₂↑ (hydrogen gas produced)
- Acid + base (neutralisation): carefully mix until neutral
- Acid + carbonate: HCl + CaCO₃ → CaCl₂ + H₂O + CO₂↑
- Precipitation: mix two soluble salts to form insoluble precipitate
Naming salts: HCl makes chlorides, H₂SO₄ makes sulphates, HNO₃ makes nitrates.
Key Points to Remember
- 1pH below 7 = acid; above 7 = alkali
- 2Neutralisation: acid + base → salt + water
- 3HCl → chlorides; H₂SO₄ → sulphates; HNO₃ → nitrates
- 4Acid + carbonate → salt + water + CO₂
Pakistan Example
Antacids in Pakistani Pharmacies — Chemistry of Indigestion
Millions of Pakistanis take Digene or ENO for acidity (stomach has excess HCl, pH ~2). Antacids contain Mg(OH)₂ or CaCO₃ — bases that neutralise acid. MgCO₃ + 2HCl → MgCl₂ + H₂O + CO₂. The fizzing you see is CO₂ gas. Lemon juice (citric acid) on daal is also an acid-base reaction — pure AKU-EB exam content.
Quick Revision Infographic
Chemistry — Quick Revision
Acids, Bases & Salts
Key Concepts
Formulas to Know
H below 7 = acid; above 7 = alkaliNeutralisation: acid + base → salt + waterHCl → chlorides; H₂SO₄ → sulphates; HNO₃ → nitratesAcid + carbonate → salt + water + CO₂Antacids in Pakistani Pharmacies — Chemistry of Indigestion
Millions of Pakistanis take Digene or ENO for acidity (stomach has excess HCl, pH ~2). Antacids contain Mg(OH)₂ or CaCO₃ — bases that neutralise acid. MgCO₃ + 2HCl → MgCl₂ + H₂O + CO₂. The fizzing you see is CO₂ gas. Lemon juice (citric acid) on daal is also an acid-base reaction — pure AKU-EB exam content.